Two of my grandsons spent the night so we watched Harry Potter and the Chamber of Secrets (2002), the second installment in the Harry Potter franchise. It had started on TV, so I threw in the DVD to start it at the beginning, and for some surround sound.
My guess for the most popular character in the series, other than the three leads, is Rubeus Hagrid, played in all of the Potter flix by Robbie Coltrane (b. 1950). He has an easy going nature and he trusts his charges to be honest. He also has a passing resemblance (except for the antithesis of hair) to Curly Howard (1903 - 1952) of the Three Stooges. Both are heavy and have a lovable, comedic personality.
I don't know if I can qualify Coltrane as a Bit Actor, but until Harry Potter and the Sorcerer's Stone (2001) he was relatively unknown in the USA, unless you were really paying attention. He has 98 roles listed on IMDb.
In his early film days, Coltrane was in Flash Gordon (1980) starring people like Max von Sydow (b. 1929), Topol (b. 1935) and Timothy Dalton (b. 1944).
He had a small part as a man in the bathroom in European Vacation (1985) starring Chevy Chase (b. 1943) and was in Revolution the same year with Al Pacino (b. 1940) and Donald Sutherland (b. 1935). He is getting small part work in good movies, and good parts in lesser movies.
In 1986 he was in Mona Lisa where he had a bigger part opposite Bob Hoskins (b. 1942) and Michael Caine (b. 1933). He has an interesting mix of roles, plus a lot of British TV, probably because he lives in England.
The part that brought him to the attention of the mainstream audience was as a former KGB agent in GoldenEye (1995), a part he reprises in 1999 for The World is not Enough. ANY James Bond film will do wonders for your acting career. He was noticed by none other than J.K. Rowling (b. 1965) herself, and at her suggestion Coltrane was cast to play Hagrid.
Of course making eight Harry Potter films in the same number of years would take a majority of your time. But Robbie Coltrane continued to work in other projects. We see him in Oceans Twelve (2004), The Brothers Bloom (2008) and he does a voice part in Tales of Despereaux, also in 2008.
He has had a hard life, worked out his problems, and made it into a complete success. It would be interesting to see how much he made, just for his part as Hagrid. I like him. He's the kind of actor I'd like to invite to dinner.